CAPE CANAVERAL, Fla. — An Air Force doctor who headed a controversial astronaut health study told Congress on Thursday that NASA is discouraging open communications by rebutting reports of drunken astronauts on launch day and deriding the claims as urban legends.

The bigger issue, more than drinking, is NASA’s apparent disregard of mental health and behavior issues among its astronauts, and the demoralizing reluctance among flight surgeons and astronauts to report improper conduct, said Col. Richard Bachmann Jr.

Last week, NASA released the results of its own internal investigation, saying it had found no evidence or even hints of astronaut intoxication before launch, contrary to what the Bachmann committee had reported a month earlier.

While defending his report, Bachmann said he understands NASA’s outrage over his medical panel’s citing of at least two instances of launch-day intoxication. Even though fellow astronauts or flight surgeons notified their bosses about the crew members’ drunken state, they were ignored, Bachmann’s committee was told confidentially.

“Public statements that such things are simply impossible, challenging the veracity of the findings, referring to them as unproven allegations or urban legends, rather than acknowledging how difficult raising such concerns can be, do not encourage openness and safety, make future reporting even less likely, and increase the risk of future mishaps or incidents,” Bachmann told the House Subcommittee on Space and Aeronautics in Washington.

NASA’s inability to find even a single case of astronaut drunkenness on launch day doesn’t prove it didn’t happen, said Bachmann, commander of the Air Force School of Aerospace Medicine. Rather, it shows only that the NASA employees who told his panel about the incidents did not bring them up during NASA’s internal review, he said.

“We believe this may represent continued fear and barriers to communication and may be a cause for greater, not less concern,” he said.

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Both the Challenger and Columbia disasters were blamed, in part, on miscommunication and broken safety cultures within the space agency.

The independent but NASA-appointed health review committee heard from astronauts and flight surgeons earlier this year who were “eyewitnesses to the events” and freely volunteered the information regarding astronaut intoxication, Bachmann said. No names or dates were included in the panel’s final report in late July.

The astronaut health review committee — established following the February arrest of astronaut Lisa Nowak in a scandalous love triangle — identified a number of cultural issues within NASA that “make it even more difficult to predict an episode of disordered conduct,” Bachmann testified.

As part of its investigation into the committee’s findings on astronaut drinking, NASA reviewed 20 years of shuttle flight records and spoke with astronauts, flight surgeons and others associated with spaceflight in both the United States and Russia. Nothing incriminating was found, officials said last week and again Thursday.

NASA Administrator Michael Griffin went so far last week as to call the claims of prelaunch astronaut drunkenness an urban legend, likening it to alarming but false reports of deliberately poisoned Halloween candy.

On Thursday, Griffin said he recognizes that the Nowak case, a murder-suicide at Johnson Space Center in Houston last spring and the allegations of alcohol abuse by astronauts has shaken public confidence in NASA. The space agency is implementing many of the health panel’s recommendations to improve medical and behavioral health care for astronauts, he said, and is taking steps to ensure that astronauts forgo alcohol in the 12 hours before launch.

NASA also plans to conduct an anonymous survey this month of its astronaut and flight surgeons in an attempt to ferret out any additional information on the drinking issue or other problems.

The 12 orbiting astronauts on the International Space Station were hailed by the chief on Thursday — and also got a humorous scolding for keeping their android crewmate locked up in its packing for so long.